Evaluation of Vascular Reactivity of Maternal Vascular Adaptations of Pregnancy With Quantitative MRI: Pilot Study

Abstract

Background: Abnormal maternal vascular function during pregnancy stemming from systemic endothelial dysfunction (EDF) has a central role in the pathophysiology of preeclampsia (PE).

Purpose: To utilize quantitative MRI to investigate changes in physiological measures of vascular reactivity during normal pregnancy, and to explore EDF associated with preeclampsia.

Study type: Prospective.

Population: Healthy pregnant (HP) (n = 14, mean GA = 26 ± 7 weeks) and nonpregnant women (NP; n = 14); newly postpartum (PP <48 hours) women with severe PE (PP-PE; n = 4) and normotensive pregnancy (PP-HP; n = 5).

Field strength/sequence: 1.5T/3T. RF spoiled multiecho gradient-recalled echo, 1D phase-contrast MRI, time-of-flight.

Assessment: The micro- and macrovascular function (vasodilatory capacity of arterioles and conduit arteries, respectively) of the femoral vascular bed was evaluated with MRI-based venous oximetry, arterial velocimetry, and luminal flow-mediated dilation quantification, during cuff-induced reactive hyperemia. Aortic arch pulse-wave velocity (aPWV) was quantified to assess arterial stiffness using an ungated 1D technique.

Statistical tests: Two-tailed unpaired t-tests were performed to address our two, primary a priori comparisons, HP vs. NP, and PP-PE vs. PP-HP. Given the pilot nature of this study, adjustments for multiple comparisons were not performed.

Results: In HP, microvascular function was attenuated compared to NP by a significant increase in the washout time (10 ± 2 vs. 8 ± 2 sec; P < 0.05) and reduced upslope (2.1 ± 0.5 vs. 3.2 ± 0.8%HbO₂ /s; P < 0.05), time of forward flow (28 ± 5 vs. 33 ± 6 sec, P < 0.05), and hyperemic index (11 ± 3 vs. 16 ± 4 cm/s² ; P < 0.05), but luminal flow-mediated dilatation (FMD_L )was comparable between HP and NP. PP-PE exhibited significant vascular dysfunction compared to PP-HP, as evidenced by differences in upslope (2.2 ± 0.6 vs. 1.3 ± 0.2%HbO₂ /s, P < 0.05), overshoot (16 ± 5 vs. 7 ± 3%HbO₂ , P < 0.05), time of forward flow (28 ± 6 vs. 15 ± 7 s, P < 0.05), and aPWV (7 ± 1 vs. 8 ± 1 m/s, P < 0.05).

Data conclusion: Attenuated vascular reactivity during pregnancy suggests that the systemic vasodilatory state partially depletes nitric oxide bioavailability. Preliminary data support the potential for MRI to identify vascular dysfunction in vivo that underlies PE. Level of Evidence 2 Technical Efficacy Stage 1 J. MAGN. RESON. IMAGING 2021;53:447-455.

Keywords: MR oximetry; MRI; endothelial dysfunction; femoral artery flow-mediated dilation; maternal vascular adaptations; preeclampsia; pulse-wave velocity; reactive hyperemia.